Non-leaching adhesive system and its use in a liquid immersion objective

ABSTRACT

A non-leaching adhesive system and its use in a liquid immersion objective for immersion-writing of masters for optical discs are disclosed. The adhesive system comprises at least one monomer, selected from among the group of acrylate and methacrylate monomers, allylic monomers, norbornene monomers, hybrid monomers thereof, containing chemically different polymerizable groups, and multifunctional thiol monomers, provided that said thiol is used in combination with at least one of said non-thiol monomers; and a polymerization initiator. At least one of said monomers, not being a thiol, is provided with at least two functional polymerizable groups to obtain a crosslinked polymer network. The polymerization initiator is preferably an initiator that can be activated both thermally and with UV radiation. The adhesive system may further contain a reactive diluent. Further the use of the present adhesive system in mounting a liquid immersion objective is disclosed.

This is a continuation of Ser. No. 10/568,837 filed Feb. 17, 2006 and isincorporated by reference herein.

The present invention relates to the field of adhesive systems, and moreparticularly to a non-leaching adhesive system, which does not leach anyharmful components or impurities into a liquid which is or becomes intocontact with said adhesive system, when it has been cured. The term‘non-leaching’ here refers to the absence of the leaching of compoundsthat are detrimental to the application in which the adhesive is used.Examples of such applications are the use in deep-UV mastering ofhigh-density optical discs, the use in deep-UV lithography of siliconwafers, the use in liquid immersion lithography and in immersionmicroscopy in the biological field. Further important applications arein the assembly of catheters and other biomedical devices forapplications likely to come into contact with fluids and tissue as wellas in the construction of biosensors, notably those which containassembled microfluidic structures. Also many applications are found inthe veterinary and food & beverage industry. It is in such applicationsof the utmost importance that the liquid which comes into contact withthe cured adhesive remains extremely pure, thus free of anycontamination.

In liquid immersion microscopy, for example, the numerical aperture (NA)and consequently the resolution of the microscope objective is increasedby applying an immersion liquid between the steady lens and a steadyobject. The adhesive forces of the liquid keep the object immersed. Whenthe object moves, however, breakdown of immersion may occur, either bypulling the liquid away from the lens or by pulling gas under theobjective. The key issue in applying liquid immersion in a dynamicsystem such as a mastering machine therefore is to maintain a stableliquid film between the stationary lens and the moving substrate.

In critical applications such as for example deep-UV mastering of highdensity (Blu-ray Disc) optical discs using a high NA liquid immersionobjective for writing of information in a photo-resist layer on a masterdisc, the proper development of the photo-resist is often impeded by alow concentration of impurities in the immersion liquid. Thiscontamination (which might be very little) is due to leaching ofimpurities from adhesives used in constructing the objective andimmersion accessory.

Usually, two-component epoxy-amine or epoxy-anhydride adhesive systemsare used. It then often occurs that alkaline impurities from theadhesive, or, when the adhesive has been dosed, mixed and/or curedimproperly, unreacted amines, leach into the water phase and next intothe resist. (Even epoxy-anhydride systems may contain leachable tertiaryamine accelerators). The aimed contrast between exposed and non-exposedareas will then, locally, be changed or even removed, showing up aspoint defects or as stains in the master disc. Such defects willthereafter also be transferred to the stampers and replicated discs madefrom such master discs.

The same problem of a partially or totally undeveloped resist has beenobserved with several positive tone resists, belonging for example tothe novolac-diazoquinone type of resists.

The present invention now provides an adhesive system which does notleach harmful impurities or components, and thus allows properdevelopment of the exposed resist layer and subsequent stampermanufacturing.

More specifically, the invention relates to a non-leaching, curable,adhesive system, comprising at least one monomer, selected from amongthe group of acrylate and methacrylate monomers, allylic monomers,norbornene monomers, mixtures of said monomers and hybrid monomerscontaining chemically different polymerizable groups in one monomer andmultifunctional thiol monomers, provided that said thiol is used incombination with at least one of said non-thiolmonomers; and apolymerization initiator. Preferably, at least one of said monomers, notbeing a thiol, is provided with at least two functional groups, whichgroups will take part in the polymerization process, to obtain acrosslinked polymer network. The term “multifunctional” as used here,means that the number of monomers which can be coupled per monomer islarger than 1.

Although virtually any monomer polymerizable by free radical initiation,can be used in the present adhesive system, those compounds arepreferred which provide a cross-linked product with good adhesiveproperties to glass and metals. It is observed that the term “glass” asused here also refers to quartz-glass.

The diacrylate monomer which is more preferably used in the presentadhesive system is2,2-bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane.

Alternatively, thiol-ene systems composed of multithiols andmultiallylic monomers and a (radical) polymerization initiator can beused, either separately or in combination with the above indicated(meth)acrylates. Non-limitative examples of thiols aretrimethylolpropane trithiol, pentaerythritol tetrathiol and theirethoxylated homologs. Non-limitative examples of allylic monomers arethe diallylic ester of isophorone diisocyanate, triallyl cyanurate and-isocyanurate and the di- and triallyl ethers of trimethylolpropane.

As indicated above, the adhesive system also contains a polymerizationinitiator. Preferably a single initiator that can be activated boththermally and with radiation, preferably UV radiation, is used.

Azobisisobutyronitrile is a good example, although many azoesters may beused as well.

Azoester-initiators have the advantage that they have, apart from theirphotochemical decomposition, a rather high decomposition rate atrelatively low temperatures, which allows their use also at low andmoderately high temperatures.

Examples of photo-initiators which decompose only at highertemperatures, and which can also be used in the present invention areα-hydroxy-ketones, such as Irgacure 184 and Darocure 1173 (bothtrademarks of Ciba-Geigy AG); α-amino-ketones, such as Irgacure 907 andIrgacure 369 (both trademarks of Ciba-Geigy AG) andbenzyldimethyl-ketal, such as Irgacure 651(=DMPA:α,α-dimethoxy-α-phenyl-acetophenone) (trademark of Ciba-GeigyAG).

The present adhesive system further comprises in an expedientembodiment, a reactive diluent. It is in this respect observed, that thedi(meth)acrylate monomers to be used in the present adhesive system mayhave a viscosity at the operation temperature of, for example, 60° C.,which is too high for proper application on the delicate substrates tobe bonded. It is in these cases preferred to use a reactive diluent.

Said reactive diluent is either a monoacrylate but preferably a di- ormultiacrylate and/or a methacrylate diluent, examples thereof are1,6-hexanediol diacrylate and tripropyleneglycol diacrylate. Furtherexamples include ethoxylated trimethylol propane tri(meth)acrylates andpentaerythritol tetra(meth)acrylates of sufficiently low viscosity.

To support the adhering properties of the present adhesive system to asubstrate, especially a metal or glass substrate, it is preferred topretreat such substrates with a proper surface activating agent. Such asurface pretreatment will aid in the prevention of delamination or othermeans of release of the adhesive from the substrate.

The invention therefore also relates to a non-leaching, curable,adhesive composition, based on monomers, comprising (a) an adhesivesystem as defined above, and (b) a surface activating agent.

Said surface activating agent is preferably an acrylic or methacrylicsilane coupling agent. These agents can be used both with (meth)acrylateand thiol-ene systems. Alternatively, a thiol or an allylic couplingagent may also be used with the thiol-ene systems. It is in this respectobserved that the use of a silane coupling agent together with anadhesive composition for bonding metal substrates is known as such fromEP-A-1 005 037. Specific examples of such a coupling agent arenevertheless missing in this reference. Further, EP-A-1 005 037 relatesto a cationic UV curable composition, preferably consisting of an epoxyresin as the main component and a cationic polymerization typephoto-initiator. Such systems are characterized by their capability ofleaching ionic compounds which are likely to affect the resist behavior.

As indicated above, the present invention relates, on the contrary, toan adhesive system based on acrylate and/or methacrylate monomers,allylic monomers, norbornene monomers, hybrid monomers of said monomerscontaining chemically different polymerizable groups, mixtures of saidmonomers and multifunctional thiol monomers, provided that said thiol isused in combination with at least one of said other, non-thiol monomers,and a polymerization initiator, which system does not leach any harmfulcomponent into a liquid which comes into contact with said adhesivesystem when it has been cured.

The methacrylic silane coupling agent of the present invention ispreferably γ-methacryloyloxypropyl trimethoxysilane.

The present invention further relates to a process for ensuring themetal-to-metal and metal-to-glass adhesion by applying a coating of anon-leaching, curable, adhesive system, as defined above, to thesurfaces of parts to be joined, joining the thus coated surfaces of saidparts and curing the combination, wherein the surfaces to be joined arepretreated with a surface activating agent before the application of theadhesive system.

Such a pretreatment will further prevent delamination and/or leakage ofwater, as has been indicated above.

The surface activating agent is preferably an acrylic or methacrylicsilane coupling agent, more preferably γ-methacryloyloxypropyltrimethoxysilane.

The pretreatment of the surface to be provided with an adhesiveaccording to the present invention consists preferably of an exposure ofsaid surface to the vapor of the coupling agent, if desired dissolved ina suitable solvent, or of a treatment of said surface with a solution ofsaid coupling agent in a suitable solvent, or any other suitableprocess.

The invention further relates to the use of the present adhesive systemfor the adhesion of a metal film to another metal film or a glasssubstrate of a liquid immersion objective, to be used for thepreparation of a substrate, in particular an optical master disc.

As has been explained before, leaching of traces of components from theadhesive, used in constructing the immersion objective and immersionaccessory, into the immersion liquid, often has the result that theproper development of the resist layer on a master disc in saidimmersion microscope is impeded. The thus obtained defects show up aspoint defects or as stains; they appear not only in the resist layer ofthe master disc, but will also be transferred to the stampers andreplicated discs made from such master discs.

The use of the present adhesive prevents this leaching problem,surprisingly, completely.

The invention further relates to a liquid immersion objective as definedin claim 16.

The above indicated and other aspects of the invention will be apparentfrom and elucidated with reference to the drawings and followingexamples, which are not to be interpreted as limiting the scope of thepresent invention in any respect.

FIGS. 1 a and 1 b show a cross-section and bottom view respectively ofthe liquid immersion concept used in optical disc mastering.

FIG. 1 c shows details of the embodiment of the immersion lens mount andwater supply accessory of FIG. 1 a.

FIG. 2 shows point defects, obtained on a replicated disc by using aconventional adhesive in the liquid immersion microscope.

FIG. 3 shows stains, obtained on a replicated disc by using aconventional adhesive in the liquid immersion objective.

FIG. 4 is an AFM picture showing point defects on the father stamperproduced by using a conventional adhesive in the liquid immersionobjective.

FIG. 5 a shows a replicated disc, obtained by using an adhesiveaccording to the invention, without stains or point defects(magnification 10×).

FIG. 5 b shows the same disc as shown in FIG. 5 a, but with amagnification of 20×.

In the set-up used for immersion-writing of master discs for Blu-raydiscs, this has been realized using the liquid immersion concept asillustrated in FIGS. 1 a, b and c.

Liquid immersion is achieved by locally maintaining a water film betweenthe final lens element 5 of the objective 6 and the rotating masteringdisc 2 with the photo-resist 4 (see FIG. 1 a). Water is a natural choicein this application for the immersion liquid as it is transparent forradiation with a wavelength of 257 nm used for writing and is compatiblewith resist processing. The objective used was a commercially availablelens (numerical aperture (NA)=0.9, λ=257 nm) that is transformed into anNA=1.23 water immersion lens by adding an almost hemispherical finallens element (not shown). The water is continuously supplied through ahole 9 just upstream of the immersion lens 5 at a pressure, sufficientlyhigh in order to avoid gas inclusion and sufficiently low to prevent therelease of dissolved gas. The bottom view in FIG. 1 b shows how therelative velocity of lens and coated disc pull the water under the lensresulting in a stable water trace around the focus position. The watertrace typically is 7 μm high and 200 μm wide at writing velocities up to5 m/s. The forces exerted by this narrow water trace on the lens 5 areminimal so that the focus actuation is not hampered by the presence ofthe water film.

The construction of the immersion lens mounting and water supply had tobe realized within the original working distance of the far fieldobjective, which is only 250 μm. This has resulted in a very slim mountfor the immersion lens, 200 μm thick only, containing a water supplychannel 8. The lens mount consists of a stack of four metal foils 7,shown in FIG. 1 c, which are shaped and glued together in such a waythat a water supply channel 8 is created.

The water passes through a hole 9 in the lower foil of the stack offoils 7 to reach the interface between objective 6 and disc 2. Thismeans that the water used for immersion is in close contact with theadhesive. The adhesive in the stack of foils 7 has to be cured thermallysince it is not accessible to UV light.

The final immersion lens element has to be firmly attached to the foilaccessory. This is also achieved by gluing. Here, a UV curable adhesiveis preferred since high temperatures are to be avoided in order toreduce the build-up of stress, relaxation thereof and consequentlyinaccurate positioning of the immersion lens element 5.

When conventional adhesives are used, such as epoxy-amine/anhydridebased adhesives, it often occurs that the resist remains partially ortotally undeveloped after rinsing or spraying with or dipping into theaqueous developer solution. The defects show up as point defects (FIG.2) or as stains (FIG. 3). The defects not only show up in the resistlayer but are also transferred to the stampers and replicated discs madefrom such masters. A detail of a point defect on a father stamper isshown in FIG. 4. The resist is locally undeveloped.

The track width in FIGS. 2 and 3 was 0.7 mm, while the track pitch inFIG. 4 was 320 nm.

FIG. 5 a and FIG. 5 b show a replicated disc produced by using animmersion microscope described in FIGS. 1 a, 1 b and 1 c, mounted byusing an adhesive according to the invention. The track width in FIGS. 5a and 5 b was 0.4 mm.

EXAMPLE 1

An adhesive was prepared by mixing a 80% (w/w) solution of2,2-Bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane (=bis-GAA) in1,6-hexanedioldiacrylate with 0.1% (b.w.) of azobisisobutyronitrile.

This adhesive was used in the lamination of the stack of foils and thegluing of the objective lens as shown in FIGS. 1 a and 1 b. The adhesivebetween the foils was cured by heating the stack of foils to 90° C. for12 h. The objective lens was fixed to the stack of foils by exposure ofthe same adhesive to UV light (wavelength range 320-390 nm, intensity 40mW.cm⁻², exposure time 1 min.).

It appeared that the adhesive system did not leach out impurities asshown by a proper development of the exposed resist layer and subsequentstamper manufacturing by means of an immersion microscope objective asshown in FIGS. 1 a, 1 b and 1 c.

The excellent quality of the adhesive system is further illustrated bythe absence of stains and pinholes on replicated discs, as shown inFIGS. 5 a and 5 b.

EXAMPLE 2

An adhesive was prepared according to Example 1, but by using bis-GAA asa 75% (w/w) solution in tripropyleneglycoldiacrylate.

The same results as indicated in Example 1 were obtained.

EXAMPLE 3

To further prevent delamination and/or leakage of water (if possible, atall), the surfaces to be bonded with each other, were subjected to apretreatment with a liquid silane coupling agent. More specifically, themetal foils and the immersion lens were placed in a desiccator, whichcontained an open vessel with γ-methacryloyloxypropyltrimethoxysilane.

The desiccator was evacuated and the metal foils and lens were exposedovernight to the vapor of said coupling agent. Thereafter the parts werebonded by using the adhesive and procedure indicated in Example 1.

Neither stains nor point defects were observed upon development ofmaster discs made using the mastering device depicted in FIG. 1 b.

COMPARATIVE EXAMPLE 1

Discs replicated from stampers made using a liquid immersion microscopesystem as outlined in FIG. 1 c that was constructed by using aconventional epoxy-amine adhesive, namely Araldite 2011 (trademark ofVantico) showed many point defects and stains as shown in FIGS. 2 and 3.The defects were already present on the stamper used for replicating thedisks (FIG. 4).

While the present invention is described with respect to specificembodiments thereof, it is recognized that various modifications andvariations thereof may be made without departing from the scope andspirit of the invention, which is more clearly understood by referenceto the claims appended hereto. Any reference signs in the claims shall,further, not be construed as limiting the scope of the invention.

1. (canceled)
 2. (canceled)
 3. The process of claim 12, wherein saidallylic monomer is selected from the group of the diallylic ester ofisophorone diisocyanate, triallyl cyanurate and -isocyanurate, and di-and triallyl ether of trimethylolpropane.
 4. The process of claim 12,wherein said multifunctional thiol is selected from the group oftrimethylolpropane trithiol, pentaerythritol tetrathiol, and theethoxylated homologs of these compounds.
 5. The process of claim 12,wherein said acrylate monomer is2,2-bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane.
 6. The processof claim 12, wherein said initiator is a photo-initiator, especially anUV initiator, a thermal initiator, or a combination of both.
 7. Theprocess of claim 12, wherein said system further comprises a reactivediluent.
 8. The process of claim 12, wherein said reactive diluent is anacrylate or a methacrylate diluent, preferably a di- or multi-acrylateor methacrylate diluent.
 9. The process of claim 12, further comprisinga surface activating agent.
 10. The process of claim 9, wherein saidsurface activating agent is an acrylic or methacrylic silane couplingagent.
 11. The process of claim 10, wherein said methacrylic silanecoupling agent is .-methacryloyloxypropyltrimethoxysilane.
 12. A processfor the metal-to-metal and metal-to-glass adhesion by applying a coatingof a curable, adhesive system, to the surfaces of parts to be joined,joining the thus coated surfaces of said parts and curing thecombination, wherein the surfaces to be joined are pretreated with asurface activating agent before the application of the adhesive system,the curable, adhesive system consisting essentially of: (1) at least onemonomer, polymerizable by free radical initiation, selected from thegroup consisting of:2,2-bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane, diallylicester of isophorone diisocyanate, triallyl cyanurate, triallylisocyanurate, and di- and tri-allyl ethers of trimethylolpropane,norbornene monomers, trimethylolpropane trithiol, pentaerythritoltetrathiol and their ethoxylated homologues, mixtures of said monomers,and hybrid monomers of said monomers containing chemically differentpolymerizable groups in one monomer; provided that when said at leastone monomer is a said thiol monomer, said thiol monomer is used incombination with at least one non-thiol monomer of said acrylatemonomers, methacrylate monomers, allylic monomers, norbornene monomers,mixtures of said monomers, and/or hybrid monomers of said monomers; and(2) a polymerization initiator, said adhesive system being anon-leaching system which, when in contact with liquid or liquid filmpresent in an application in which the cured adhesive system is used,does not leach compounds that are detrimental to the application.
 13. Aprocess according to claim 12, wherein said surface activating agent isan acrylic or methacrylic silane coupling agent.
 14. A process accordingto claim 13, wherein said methacrylic silane coupling agent is.-methacryloyloxypropyltrimethoxysilane.
 15. Use of a curable, adhesivesystem, based on monomers for the adhesion of a metal film to anothermetal film or a glass substrate of a liquid immersion objective, to beused for the preparation of a substrate, in particular an optical masterdisc the curable, adhesive system consisting essentially of: (1) atleast one monomer, polymerizable by free radical initiation, selectedfrom the group consisting of:2,2-bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane, diallylicester of isophorone diisocyanate, triallyl cyanurate, triallylisocyanurate, and di- and tri-allyl ethers of trimethylolpropane,norbornene monomers, trimethylolpropane trithiol, pentaerythritoltetrathiol and their ethoxylated homologues, mixtures of said monomers,and hybrid monomers of said monomers containing chemically differentpolymerizable groups in one monomer; provided that when said at leastone monomer is a said thiol monomer, said thiol monomer is used incombination with at least one non-thiol monomer of said acrylatemonomers, methacrylate monomers, allylic monomers, norbornene monomers,mixtures of said monomers, and/or hybrid monomers of said monomers; and(2) a polymerization initiator, said adhesive system being anon-leaching system which, when in contact with liquid or liquid filmpresent in an application in which the cured adhesive system is used,does not leach compounds that are detrimental to the application.
 16. Aliquid immersion objective, to be used for the preparation of asubstrate, in particular an optical master disc, comprising a stack ofmetal films (8), an immersion objective lens (5), being provided in athrough-hole (9), in said stack of metal films, and a substrate (2),being provided with a photo-resist layer (4) facing the immersion lens(5), said photo-resist layer and the immersion lens being separated by awater film (1), the water supply channel (3) thereof being providedbetween and through said stack of metal films (8) such that said watersupply channel discharges into the interface between said objective lensand said substrate, said metal films and immersion lens being mutuallybonded by means of a curable, adhesive system the curable, adhesivesystem consisting essentially of: (1) at least one monomer,polymerizable by free radical initiation, selected from the groupconsisting of: 2,2-bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane, diallylicester of isophorone diisocyanate, triallyl cyanurate, triallylisocyanurate, and di- and tri-allyl ethers of trimethylolpropane,norbornene monomers, trimethylolpropane trithiol, pentaerythritoltetrathiol and their ethoxylated homologues, mixtures of said monomers,and hybrid monomers of said monomers containing chemically differentpolymerizable groups in one monomer; provided that when said at leastone monomer is a said thiol monomer, said thiol monomer is used incombination with at least one non-thiol monomer of said acrylatemonomers, methacrylate monomers, allylic monomers, norbornene monomers,mixtures of said monomers, and/or hybrid monomers of said monomers; and(2) a polymerization initiator, said adhesive system being anon-leaching system which, when in contact with liquid or liquid filmpresent in an application in which the cured adhesive system is used,does not leach compounds that are detrimental to the application. 17.Use of a non-leaching, curable, adhesive system for the mutual adhesionof at least two bodies, selected from among the group, consisting ofmetal films, (quartz-)glass substrates, and polymeric films, for themanufacturing and/or assembling of catheters, biosensors and otherbiomedical devices likely to come into contact with fluids and tissue,the curable, adhesive system consisting essentially of: (1) at least onemonomer, polymerizable by free radical initiation, selected from thegroup consisting of:2,2-bis[4-(3-acryloyloxy-2-hydroxypropoxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane, diallylicester of isophorone diisocyanate, triallyl cyanurate, triallylisocyanurate, and di- and tri-allyl ethers of trimethylolpropane,norbornene monomers, trimethylolpropane trithiol, pentaerythritoltetrathiol and their ethoxylated homologues, mixtures of said monomers,and hybrid monomers of said monomers containing chemically differentpolymerizable groups in one monomer; provided that when said at leastone monomer is a said thiol monomer, said thiol monomer is used incombination with at least one non-thiol monomer of said acrylatemonomers, methacrylate monomers, allylic monomers, norbornene monomers,mixtures of said monomers, and/or hybrid monomers of said monomers; and(2) a polymerization initiator, said adhesive system being anon-leaching system which, when in contact with liquid or liquid filmpresent in an application in which the cured adhesive system is used,does not leach compounds that are detrimental to the application.